This has been a rampant problem on Wikipedia always. I can't seem to find any indicator that this has increased recently? Because they're only even investigating articles flagged as potentially AI. So what's the control baseline rate here?
Applying correct citations is actually really hard work, even when you know the material thoroughly. I just assume people write stuff they know from their field, then mostly look to add the minimum number of plausible citations after the fact, and then most people never check them, and everyone seems to just accept it's better than nothing. But I also suppose it depends on how niche the page is, and which field it's in.